Compounds of formula (I) have antibacterial activity: wherein: m is 0 or 1; Q is hydrogen or cyclopropyl; Alk is an optionally substituted, divalent C1-C6 alkylene, alkenylene or alkynylene radical which may contain an ether (—O—), thioether (—S—) or amino (—NR)— link, wherein R is hydrogen, —CN or C1-C3 alkyl; X is —C(═O)NR6—, —S(O)NR6—, —C(═O)O— or —S(═O)O— wherein R6 is hydrogen, optionally substituted C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, -Cyc, or —(C1-C3 alkyl)-Cyc wherein Cyc is optionally substituted monocyclic carbocyclic or heterocyclic having 3-7 ring atoms; Z is N or CH, or CF; R2 and R3 are as defined in the description.